Automotive seats have been made of supported and covered open cell polyurethane foam cushions. The molded cushion is supported by a suitable frame which may include wire or other support portions underlying the foam or embedded in it. Two or more different foams may be used to provide the cushion(s) with regions of different stiffness or hardness for seating comfort. The seating surface and sides of the cushion are covered with a decorative, usually colored material. The cover material, for example, may be a vinyl sheet leather or a woven or knit cloth fabric. The cover material is usually attached to the foam bun and/or to the frame by suitable connectors such as hog rings, hooks and loops or other mechanical fasteners. In some automobile seats a multilayer seat cover assembly, including a relatively thin foam layer, is used to cover the seat cushions. As will become apparent the multilayer cover makes it easier to provide decorative or functional lifts or contours in the seating surface or back surface of the seat. Generally, these assemblies comprise at least three layers. Typically, a relatively thin cloth layer (e.g. a scrim material) serves as a base layer. An intermediate layer is a thin (up to about 1/2 inch), flexible, polyurethane foam pad. The outer layer is a decorative cover of, for example, vinyl sheet or a suitable fabric. The three layers are usually sewn together by adhesive material.
Sometimes it is desired to form decorative or functional contours, or lifts, or embossments in the visible surface of these laminated cover assemblies or pads. One way to do this is to laboriously press down and stitch the cover layer to the base layer. Often a more efficient way would be by die bonding or by dielectric embossing.
In dielectric embossing a two-platen press is used with a suitable die(s) to form the desired pattern of indentations (embossments) into the cover surface of the seat cover assembly. Under each die edge the foam is essentially fully compressed and the cover layer brought close to the base layer. A very high frequency (typically radio frequency) electromagnetic field is applied between the platens to the workpiece. Any material in the workpiece that is responsive to the high frequency field will be quickly heated. In this case the goal is to heat and fuse the polyurethane foam compressed under the die edges and between the cover layer and substrate. Upon solidification, the fused foam bonds the cover layer to the substrate, retaining the desired embossed pattern in the trim member.
Conventional polyurethane foam slab stock is not readily heated dielectrically. It is not a dielectrically "lossy" material. However, polyurethane foam compositions have been formulated or prepared which can be dielectrically heated and such materials have been used in relatively thin, dielectrically embossed, laminated seat cover assemblies. However, the embossed polyurethane seams are quite stiff if they include much fused foam. Such stiffness is undesirable in automotive seats. Furthermore, if the foam layer is very thick, the embossed structure is distorted. Heretofore, the urethane foam dielectric embossing technology has not permitted the decorative embossing of a relatively thick, urethane foam layer such as may be required or desired in a seat cover assembly.
Accordingly, it is an object of the present invention to provide a method of making decorative, dielectrically embossed, urethane foam seat cover assemblies where the embossed pattern can be formed without regard to the overall thickness requirements of the foam layer of the assembly.